Impulse sending arrangement for use in telephone or like systems



Oct. 14, 1941. wRlGHT 2,259,334

IMPULSE SENDING ARRANGEMENT FOR USE IN TELEPHONE OR LIKE SYSTEMS Filed July 28, 1938 [N VENT'OR N/S WR/GHT' A TTOR/Y E Y Patented Oct. 14, 1941 IMPULSE SENDING ARRANGEMENT FOR USE IN TELEPHONE OR LIKE SYSTEMS Denis Wright, Liverpool, England, assignor to Associated Telephone & Telegraph Company,

Chicago, 111., a corporation of Delaware Application July 28, 1938, Serial No. 221,667 In Great Britain August 25, 1937 2 Claims.

The present invention relates to impulse sending arrangements for use in automatic telephone or like systems in which control operations are eliected by trains of similar impulses, the number of impulses in a train varying in accordance with the effect it is desired to produce. The invention moreover is primarily concerned with impulse senders of the dial type of the mechanical construction ordinarily used in such systems. The chief object of the invention is to provide an arrangement whereby such devices may be modified to enable alternating current impulses at a predetermined frequency to be directly produced from a direct current source.

According to one feature of the invention in an impulse sender for use in telephone or like impulse sending systems the rotatable cam for generating the impulses has a contour such that the impulse springs are repeatedly opened and closed during each impulse.

According to another feature of the invention in an impulse sender for use in telephone or like impulse sending systems impulses are generated by a rotatable cam controlling a movable contact spring normally located in a central position and adapted to be repeatedly operated in both directions during each impulse to engage with suitable fixed contact springs.

A further feature of the invention is that in an impulse sending arrangement for use in telephone or like systems the impulse springs are connected so that for each impulse their operation produces pulsating direct current which is converted to alternating current by the use of a suitable transformer.

Still another feature of the invention is that in an impulse sending arrangement for use in telephone or like systems alternating current impulses are generated from a local source of direct current by the use of an impulse sender of known type provided with an impulse cam of special contour in association with a transformer.

According to a further feature of the invention in an impulse sending arrangement for use in telephone or like systems the impulse sender is arranged to complete circuits alternately for the two halves of the centre-tapped primary Winding of a transformer so that alternating current impulses are obtained from the secondary of the transformer.

The invention will be better understood from the following description of an application of the invention to an automatic telephone subscribers impulse sender of the dial type such as is disclosed in United States Patent No. 1,642,822 granted Sept. 20, 1927, to Herbert F. Obergfell. In this form of impulse sender the moving spring of the impulsing spring set which comprises a pair of normally closed contacts rides on the periphery of a rotatable cam, one revolution of which produces two impulses. The rate of impulsing is normally ten impulses per second so that thecam rotates at a speed of five revolutions per second and the contour of the cam ensures a. predetermined ratio of make to break" for each impulse.

The accompanying drawing shows the impulsing spring set and the associated operating cam of a dial such as disclosed in the before-mentioned patent since these are the only two modified items of the mechanism, the method of operation and of speed control remaining unaltered. The drawing also shows the circuit arrangement for generating impulses of alternating current according to the invention.

It will be seen that in the normal position (as shown) of the cam ID, the moving spring of the impulsing spring set II is clear of both its cooperating fixed springs so that there is no current now from the battery I2 through the left hand primary winding of the transformer i3.

The periphery of the cam I0 is so shaped that one revolution produces as before two impulses each lasting one hundred milliseconds, but in the break period of each impulse which corresponds to the make period of an ordinary direct current impulse sender the impulsing contacts are all separated, while in the make period a vibratory direct current is produced in the primary winding of the transformer I3 by the riding of the moving spring of the impulsing spring set ll over a sector of six cam teeth in succession.

Regarding the dividing up of the cam periphery it may be assumed that it is equally divided up into a total of twenty teeth, ten for each impulse, and that in order to provide a make to break ratio of two to one, which is the usual ratio adopted for alternating current impulsing, four of the teeth in each set of ten are replaced by the half-height sectors I 4 and I5.

Hence in each impulse the springs II are held apart for one third of the time while in the remaining two thirds which constitutes the make period, the centre spring of the spring set H rides over the cam teeth and in so doing it connects with the upper contact six times and with the lower contact seven times, corresponding to a frequency of vibration of one hundred cycles per second. During this make period therefore,

the upper and lower halves of the transformer l3 are alternately energised momentarily and hence an alternating current is produced in the secondary winding which has a. frequency of one hundred cycles per second and the potential of which is dependent on the turns ratio of the transformer windings and the E. M. F. of the local battery l2. The alternating current thus produced is suitably applied to the line extending to the distant apparatus which may be arranged to respond thereto in any known orsuitable manner.

The make to break ratio of each impulse, and the frequency of the alternating current generated may be readily set at any value by the substitution of an appropriately cut cam in the impulse sending mechanism. a

The earthed series connected resistances l6 and I! and associated condensers l8 and [9 which are connected to the upper and lowersprings of the impulsing spring set ll serve-to eliminate destructive arcing at the contacts and also tend to improve the wave form of the alternating current generated in the transformer.

The arrangement described may find application in an automatic telephone system in which some of the telephone instruments are in isolated situations at a great distance from the telephone exchange. Under these circumstances the usual direct current dialling arrangements may not be efiicient enough, but the adoption of the invention enables the advantages of alternating current impulsing to be had even though there is no alternating current mains supply available at the calling point.

The invention might also be utilised in connection with systems in which the selective calling from a central point of the various stations connected in a series loop circuit normally traversed by direct current is effected by the superimposition of a train of alternating current impulses thereon, interruption of the direct current circuit being normally used for signalling to the central point. Such a system might be employed for instance for providing selective police call facilities in association with a fire alarm loop system.

Furthermore the invention may be applied not only to dial switches but to systems employing mechanical impulse storing and regenerating devices as described in J. W. McCleW and C. R. Woodlands application, Serial No. 79,830, filed May 15, 1936, so that received direct current impulses may be retransmitted as alternating current impulses.

In cases where it is desired to generate impulses of alternating current at a relatively high frequency, for instance of the order of 800 cycles per second some difficulty would probably be experienced in using the arrangement described. In these circumstances arrangements might be made to couple the diaphragm of a small microphone to a spring member which bears against the periphery of the rotatable cam, the microphone being connected in a direct current circuit which includes the primary winding of the transformer. On vibration of the spring in response to rotation of the cam, the microphone Will vary its resistance in sympathy and so produce a vibratory direct current in the primary winding of the transformer which in turn sets up an alternating current in the secondary winding.

I claim:

1. In an impulse sender, a sending circuit, impulse springs, a rotating cam controlling the op eration of said springs, said cam having part but not all of its periphery serrated, and means controlled by said springs for transmitting over said circuit during each revolution of the cam an impulse comprising a.plura1ity of complete cycles of alternating current and corresponding in length to the length of the serrated part of said cam.

2. In an impulse sender, a sending circuit, impulse springs, a rotating cam controlling the operation of said springs, a plurality of groups of serrations on said cam, the serrations in each group being spaced uniformly and adjacent groups of serrations being spaced farther apart than are adjacent serrations within the groups, and means controlled by said springs for transmitting over said circuit an impulse of alternating current corresponding to each of said groups of serrations.

DENIS WRIGHT. 

